Electrospinning Organometallics to Produce Metallic … · Electrospinning Organometallics to...

Project Number: SYS - 2007

Electrospinning Organometallics

to Produce Metallic Fibers

A Major Qualifying Project Report

Submitted to the Faculty

of the

WORCESTER POLYTECHNIC INSTITUTE

in partial fulfillment of the requirements for the

Degree of Bachelor of Science

in Mechanical Engineering

by

Brendan Malloy

________________________________

Date: April 2008

Approved:

_______________________________

Prof. Satya Shivkumar, Major Advisor

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Table of Contents

Abstract ............................................................................................................................... 3 1. Introduction ................................................................................................................. 4 2. Background ................................................................................................................. 5

2.1 Uses of Metallic Fibrous Structures .......................................................................... 5 2.2 Production of Fibrous Structures .............................................................................. 7

2.2.1 Novel Methods for Producing Fibers ................................................................. 8 2.2.2 Electrospinning ................................................................................................ 11 2.2.3 Organometallics ............................................................................................... 13 2.2.4 Electrospinning of Metallic Fibers................................................................... 13

3. Objectives ................................................................................................................. 15

4. Experimental Design ................................................................................................. 15

5. Methodology ............................................................................................................. 19

5.1 Degradation Analysis ............................................................................................. 19

5.2 Electrospinning ...................................................................................................... 21 6. Results ....................................................................................................................... 22

6.1 Degradation Analysis .............................................................................................. 22

6.1.1 Differential Scanning Calorimeter ................................................................... 26 6.1.2 X-Ray Diffraction ............................................................................................ 28

6.2 Electrospinning ....................................................................................................... 28 6.2.1 Solution 1 - 10% PVA (Mw 146,000 – 186,000), 20% Surfactant, and 5%

Organotin .................................................................................................................. 29

6.2.2 Solution 2 - 8% PS (Mw 400,000), 2% Organotin in 1mL Ethyl Acetate ...... 30 6.2.3 Solution 3 - 0.5% Organotin in 1mL Ethyl Acetate........................................ 33

6.2.4 Solution 4 – 2% Organotin in 0.4 HCl and 0.5 Ethanol ................................. 35

6.2.5 Solution 5 - 12% PS (Mw 400,000), 2% Organotin, 1mL Ethyl Acetate ....... 35

6.2.6 Solution 6 - 5% Organotin in 1mL Ethyl Acetate........................................... 37 6.2.7 Solution 7 - 2% Organotin in 0.2mL HCl and 1mL Dimethylformamide ...... 38

8. Conclusion and Future Work ........................................................................................ 40

References ......................................................................................................................... 42 Appendix A ....................................................................................................................... 44

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Abstract

The goal of this project was to fabricate nanowires by electrospinning an organometallic

solution and burning off the organic component of the compound. The degradation

properties of the organometallic were observed by direct heating in a furnace, differential

scanning calorimetry, x-ray diffraction and energy dispersive spectroscopy. Several

different solutions were electrospun resulting in the formation of both fibrous meshes and

spray coatings. Solutions containing a polymer displayed significant improvement in

viscoelastic properties, resulting in improved electrospinnability. After thermal

degradation, EDS analysis confirmed the presence of tin and tin oxide structures. The

addition of binding agents could facilitate the formation of more complex tin

microstructures.

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1. Introduction

The field of nanotechnology has existed ever since the invention of the first electronic

devices. The promise of applying nanotechnology to medical treatment and the scaling

down of electronics, along with general miniaturization, has lead to a boom in the

development of this rapidly growing field [1]. The simple act of changing the size of a

structure can have profound effects on physical properties such as melting point,

electrical conductivity, and magnetic properties [1]. Material purity maximizes due to the

inherent lack of defects when working at such small scales. These new properties can

lead to more diverse applications. The ability to apply existing technology to the

development of nanomaterials could significantly facilitate research. One such

technology whose application could be expanded is electrospinning.

Electrospinning has already been used for years to produce polymer nanofibers

[1-4]. If electrospinning could be utilized to fabricate metallic fibers, completely new

materials possessing unique physical structures and properties could be produced. These

materials could see a variety of applications in their stand-alone form, such as filtration,

or they could be incorporated into composite materials. This study investigated the

fabrication of metal/metal-oxide fibers by means of electrospinning an organometallic

compound. The degradation properties of the chosen organometallic were analyzed by

thermally degrading the compound in a furnace, differential scanning calorimeter, x-ray

diffraction and energy-dispersive spectroscopy. The structures formed by electrospinning

different organometallic solutions were analyzed using a scanning electron microscope.

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2. Background

2.1 Uses of Metallic Fibrous Structures

Metal bars and fibers have been used for decades to imbue existing materials with

superior mechanical properties. Steel rebar can be seen in use every day to reinforce

concrete structures. This same concept is applied, albeit at a much smaller scale,

when metal and ceramic fibers are used as composite matrices in the fabrication of

metal parts. These metal matrix composites can significantly improve frictional

properties, wear resistance, strength and thermal diffusivity [5-7].

Modern disc-brakes are composed primarily of cast iron or ceramic. Steel fibers

are incorporated into the cast to form a composite that offers much higher wear

resistance [7]. However, these steel fibers can result in aggressive warping of the disc

due to the high heats generated. Copper and aluminum fibers are often added to

improve thermal diffusivity and maintain the coefficient of friction at high

temperatures.

Other metal and ceramic fibers have been used to form composite materials for

use in other parts of automobiles such as engine blocks, pistons, cylinder liners and

driveshaft [5,6]. Table 1 shows a variety of potential applications of metal and

ceramic fiber composites.

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Table i - Selected Potential Applications of Cast Metal Matrix Composites [5]

Composite Application Special Features

Gr / Al Bearings

Cheaper, lighter, self-lubricating; conserves Cu, Pb, Sn, Zn, etc.

Gr/Al, SiC-Al2O3/Al fiber, Al/FP

Automobile Pistons, cylinder liners, piston rings, connecting rods

Reduced wear, anti-seizing, cold start, lighter, conserves fuel, improves efficiency

Gr / Cu Sliding electrical contacts Excellent conductivity and anti seizing properties

SiC / Al Turbocharger impellers High temperature use

Glass or Carbon bubbles in Al Ultralight materials

Cast Carbon / Mg Fiber Composites

Tubular composites for space structures

Zero thermal expansion, high temperature strength, good specific strength and stiffness

Zircon/Al, SiC/Al, SiO2/Al Cutting tools, machine shrouds, impellers

Hard, abrasion resistant materials

Al-char, Al-clay Low cost, low energy materials

The fabrication of micro- and nano-fibers can result in the formation of porous

structures. These structures exhibit high surface area which can be utilized for use as

heat exchangers [8]. L. Tadrist et al. [8] have found that these porous structures

possess unique characteristics leading to strong thermal performance. The use of a

metallic matrix showed higher heat transfer than standard heat fins.

The porous nature of fibrous structures can also be utilized for filtration. Fibrous

bed filtration has been found to be an effective and efficient method for removing fine

dust from gas flows [9]. Filters composed of metallic fibers are desirable for use in

high temperature environments. Also, while standard flat filters use surface filtration

to stop particles, a fibrous bed can catch particles on the surface and inside the body

of the filter. Very fine particles that would otherwise travel through the filter can be

captured by electrostatic forces generated by the metal.

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2.2 Production of Fibrous Structures

Large diameter metal fibers such as rebar are produced by pouring molten metal

in to casts. Smaller diameter metal fibers are typically fabricated by wire drawing. In

this process, a cylindrically shaped piece of stock metal is pulled through a die,

reducing the cross-sectional area. The sample is drawn through successively smaller

dies until the desired fiber diameter is reached [10].

Powder metallurgy (P/M) offers a method of part fabrication that allows the

porosity to be controlled. Metal powders are produced through a variety of methods

including atomization, reduction, and electrolytic deposition. These powders are

pressed into a mold of the desired part, forming a green compact. The size and shape

of the powder particles, combined with the pressured applied in the mold, dictate the

density and porosity of the final part [10]. The compact is then sintered at a

temperature lower than the

melting point, but high enough to

allow bonding, resulting in the

formation of the final part.

A newer method for

producing porous, metal fiber

structures, like those shown in

Figure 1, is metal foam. The foams are made by combining an alloy, usually

aluminum or zinc, with a titanium or zirconium hydride, which results in a uniform,

foam-like substance [11]. This material is typically used for absorbing shock impacts

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without elastic rebounds and can be used as a substitute in some metal parts in order

to reduce weight.

2.2.1 Novel Methods for Producing Fibers

In the pursuit of producing fibers on

increasingly smaller scales, several

unique methods of micro- and nanowire

fabrication have been developed. Figure

2 shows an example of one such method.

Electron beam lithography is a standard

technique used for nanometer scale

patterning [12]. During this process, EBL is used to produce a mask, ~90nm wide, on

the surface of an Si or SiGe substrate. Anisotropic wet etching is then used to remove

layers of the underlying substrate along the (111) direction. The area under the mask

is then etched, forming an inverted V-groove shaped wire. Wires as small as 60nm

have been produced using this

method.

Another method utilizing a

similar etching process has also been

developed to produce Si/SiGe

nanowires [12]. A thin aluminum

film is sputter coated on the surface

of a Si/SiGe substrate. By operating an atomic force microscope (AFM) in “contact-

mode” with a silicon probe, oxidation can be controlled to form patterns on a metallic

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sample. Using appropriate voltage and scanning rates, aluminum oxide lines are

patterned on the surface of the substrate. Increasing voltage increased the depth of

oxidation. Chemical etching can then be applied to remove either the oxide lines or

the remaining aluminum film. Further etching removes the underlying substrate

forming Si/SiGe nanowires as small as 60nm. An outline of this process is shown in

Figure 3.

Figure 4 shows a radically different approach to nanowire fabrication [13].

Two gold (Au) electrodes were fabricated on a silicon substrate using EBL techniques.

The gap between the electrode tips was on the sub-micrometer range (20-500nm). A

solution containing Au nanoparticles of diameters ranging from 10-100nm was also

prepared. By applying appropriate AC voltages, Au nanoparticles were trapped

between the electrodes and fused together, forming particle chains or nanowires

depending upon the series impedance. Using this method allows control over both

the diameter and width of the nanostructures produced. SEM photographs of the

process are shown in figure 5.

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Nanowires have also been successfully produced using a process analogous to

casting [14]. Pores were formed in a 99% pure aluminum substrate by treatment in

phosphoric acid. The average pore diameter and length was 200nm and 50μm,

respectively. The substrate was then placed in a zirconia-based sol-gel, causing the

sol to fill the pores. Excess sol-gel was removed by polishing after the substrate had

dried. Figure 6 shows the resulting nanowires.

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H. Y. Dang et al. [15] show an incredibly simple and equally effective method of

producing metal oxide nanofibers by heating metal powder. Zinc powder was placed

in a quartz tube and placed in a tube furnace. A protective argon atmosphere was

provided until the sample was heated to just above its melting point, upon which time

and 20% oxygen and 80% argon atmosphere was substituted. The resulting fibers,

shown in Figure 7, were collected from the surface of the original powder sample.

The fibers were single crystals of uniform structure with an average diameter of 40nm

and were up to tens of micrometers long. This process also worked when used on

magnesium and germanium powders.

2.2.2 Electrospinning

Electrospinning is a long existing technology originally developed for the

fabrication of ultrathin, continuous, non-woven polymer fibers [1-4]. Figure 8 shows

a typical electrospinning apparatus.

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During the process, a high voltage source inputs and charge on the tip of a

needle/spinneret containing a polymer solution or melt. The difference in polarity

between the solution and the grounded collection plate cause electrostatic forces.

When these forces overcome the surface tension of the solution/melt in the needle, a

polymer fiber is ejected. While the fiber travels from needle to the collection plate,

much of the solvent evaporates [2]. The

fiber also elongates, causing the diameter to

shrink, due to unstable electrical forces

causing the jet to bend, whip and split

during transit [4]. By the time the fibers

collect on the plate, their diameter thins to

the micro- and nanometer range. Over 30

polymers have been successfully

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electrospun, producing fibers on the range of 40-500nm [1]. Figure 9 shows the

fibers resulting from the successful electrospinning of a polystyrene solution.

Applications of electrospun fibers include scaffolding for tissue engineering, drug

delivery, filtration, protective clothing, and wound dressings.

2.2.3 Organometallics

An organometallic compound is defined as chemical compound where a metal is

covalently bonded to carbon, although exceptions do exist [16]. While wide spread

use of these compounds is limited because of toxicity, they are very useful when

applied as catalysts. Organotins in particular are commonly used for polymer-

stabilization and as polymerization catalysts as well as for biocidal applications

(destroying microorganisms, insects, and plants) [17,18]. Organometallics are also

soluble in most organic solvents, which is why this project is investigating their use

in electrospinning. This solubility provides a simple and interesting method for

getting a metal into solution.

2.2.4 Electrospinning of Metallic Fibers

The successful synthesis of tin oxide (SnO2) fibers by electrospinning has been

published by Wang et al [19]. The research group made a tin oxide sol-gel from

anhydrous tin (IV) chloriline (SnCl4). The sol-gel was mixed with poly(ethylene

oxide) (Mw 900,000) and chloroform to form a homogeneous precursor solution.

Thermal decomposition produced SnO2 fibers with diameters ranging from 100nm to

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several micrometers. Figure 10 shows a single fiber before and after sintering at 600

C.

Porous anatase titania nanofibers have also been successfully produced by

electrospinning an ethanol solution containing titanium tetraisopropoxide and

poly(vinyl pyrrolidone) (PVP) [1].

Figure 11 shows the resulting PVP/TiO2 composite nanofibers that formed as well as

the porous TiO2 fibers that remained after pyrolysis of the PVP at 500 C.

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3. Objectives

To identify a suitable organometallic for use in producing metal or metal

oxide fibers

To examine the thermal degradation characteristics of the chosen

organometallic

To electrospin the chosen organometallic and analyze the structures

formed

To thermally degrade the electrospun structures to form metal or metal

oxide fibers

To examine the feasibility of producing nano-alloy fibers by mixing

organometallics

4. Experimental Design

Figure 12 shows the experimental design used in this study.

Choosing the organometallic that was used in this study was one of the most

important choices made during the development of this project. The criteria used for the

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selection of the material were melting point, molecular structure and price. A melting

point between 100 C and 350 C was considered most desirable as this range was

relatively low, making the material easier to handle and test, but high enough that the

degradation temperature was higher than those of the polymers that would be used in

several of the solutions. The molecular structure of the material can have a significant

effect on the properties of the material. Tetraphenyllead, an organometallic considered

for use in this study, has the molecular structure shown in figure 13.

This organometallic’s melting point is 227 C,

well within the chosen range. However, the

four phenyl rings surrounding the lead atom

make this particular compound undesirable.

The bond formed by a phenyl ring is very

strong and can require significant heating

above the material’s melting point before

degradation begins. Organometallics without these types of structures were given

preference during the selection process. Price became the most limiting variable in the

selection of the organometallic as the project budget was small and these types of

materials can be very expensive.

After considering all these criteria, a

purchase of butyltin chloride

dihydroxide was made from Sigma-

Aldrich Co. This organotin was the

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best valued organometallic available at $34 for 100g, had a melting point of 150 C and

had an acceptable molecular structure.

The preliminary method used to investigate the degradation of the organometallic

compound was to heat the powder in a furnace. This provided two important pieces of

information. First, the physical reaction of the material to thermal degradation could be

observed. If the organometallic reacted violently when heat was applied, then it would be

unlikely that any structure formed after electrospinning would survive the degradation

step that followed. This test also measured the total weight loss of the compound when

held at a constant temperature. The temperatures chosen for this test reflected the known

properties of the organometallic being used. Butyltin chloride dihydroxide had a melting

temperature of 150 C and the base metal of the compound, tin, had a melting point of 231

C. 200 C was the chosen starting temperature as it seemed sufficiently high to cause

degradation while also staying under the melting point of the tin. Exceeding the melting

temperature of the base metal could accelerate oxidation or cause the metal itself to

degrade, which could affect the results. Data were also collected above tin’s melting

point at 250 C, 300 C, 400 C, 500 C and 600 C.

A differential scanning calorimeter

(Perkin Elmer DSC 7, Figure 16) was

used to verify data gathered from the

above degradation analysis. The

sample in the DSC is heated linearly

over a range of temperatures and the

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amount of heat necessary to increase the temperature of the sample is recorded. The

resulting model can show phase transitions, which are important to understanding the

behavior of the organometallic under heating. The model generated by this scan was

used in conjunction with the previously gathered data to choose the temperature at which

the electrospun samples were degraded.

Other important methods for examining the degradation of the organometallic

were x-ray diffraction (XRD) and Energy-dispersive x-ray spectroscopy (EDS). By

utilizing these tests, the product of the degraded organometallic powder and electrospun

fibers could be identified.

In order to investigate the electrospinnability of the organometallic compound,

two types of solutions were tested. One solution was polymer based and the other

solution was primarily composed of organic solvent. Electrospinning a solution

containing both a polymer and the organometallic seemed appropriate as the use of

polymer solutions in this process has been done for decades with well documented

success. The polymer was intended to spin into a fibrous mesh and, if the organometallic

is sufficiently dissolved, hold the organotin powder in the shape of a fiber. From here,

the polymer and organic component of the organometallic would be burned off, ideally

leaving behind a metal and/or a metal oxide strand.

Introducing extra additives such as polymers to a solution can result in

complications. The polymer must be soluble in the same solvent as the organometallic

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and the polymer must also degrade at a sufficiently low temperature so as to not influence

the intended degradation temperature. Polymers could also leave carbon residues upon

degradation, which would inhibit the ability to determine results of an electrospinning

trial. To negate this possibility, solutions composed only of the organometallic and an

appropriate solvent were also tested. However, not containing a polymer can lack

sufficient viscosity to be effectively electrospun, resulting in the liquid spraying out of

the needle instead of being extruded as a fiber.

Samples obtained by electrospinning both types of solutions were analyzed by

scanning electron microscope (SEM). This analysis helped realize the electrospinnability

of each type of solution. The samples were then thermally degraded and analyzed again

in the SEM in order to observe whether or not metal or metal oxide fibers had been

successfully produced.

5. Methodology

5.1 Degradation Analysis

Aluminum foil was molded into small cups and

their initial mass was measured on a scale (Denver

Instrument Company, A-250. See Figure 16). Butyltin

chloride dihydroxide powder (96% purity) was placed in a

cup and the mass was measured again in order to

determine the initial mass of the sample. The cup was the

inserted into a furnace (Thermolyne 47900, Figure 17) set

at 200 C. The sample was heated for five minutes increments before being removed and

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allowed to cool. Placing the sample on the scale while it was

still hot produced an unstable measurement. The sample was

heated, cooled and measured until no discernable change in

mass could be determined. This test was repeated for furnace

temperatures of 175 C, 250 C, 300 C, 400 C, 500 C, and 600

C. During this process, the behavior of the compound during

heating was observed and the percent weight loss over time

was calculated.

DSC analysis was performed by preparing 3.1mg and 3.3 mg samples of

organotin powder in small aluminum specimen holders. A temperature range of 15 C to

450 C was selected. Heating was set to take place at 10 C per minute and the DSC was

left to complete the scan.

Degradation analysis was completed by performing x-ray diffraction. A sample

of the degraded powder from the weight loss test was placed into an aluminum holder

and secured into the XRD machine. The sample was set to run from 20 to 150 degrees.

The scan took approximately 30 minutes to complete.

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5.2 Electrospinning

For the electrospinning stage of the experiment, several solutions, shown in Table 2

were prepared.

Table ii - Solutions used for electrospinning trials

Each of the solutions were placed into syringes equipped with 30 gauge needles, except

for solution 1 which was also electrospun using an 18 gauge needle. For each run, a

syringe was mounted horizontally on a syringe pump (EW-74900-00, Cole-Parmer) that

was calibrated to achieve a flow rate of 1mL/hr. The high voltage power supply was set

to 10kV and the collection plate was placed 10cm from the tip of the needle for all

experiments. Each electrospinning session took place at room temperature (68-74 F) and

between 23% and 27% humidity. The needle tip and collection plate were both contained

within a plexiglas chamber for the entirety of each electrospinning run. Each of the

resulting samples were left to dry for at least twelve hours before being cut into segments

for analysis in the scanning electron microscope or degradation in the furnace at 300 C.

The electrospinning apparatus used is show in Figure 18.

Solution

1 2 3 4 5 6 7

1g Polyvinyl Acetate

0.08g Polystyrene

0.005g Organotin

0.02g Organotin

0.12g Polystyrene

0.05g Organotin

0.2g Organotin

2g SDS (Surfactant)

0.02g Organotin

1mL Ethyl Acetate 0.4mL HCl

0.02 Organotin

1mL Ethyl Acetate 0.2mL HCl

0.5g Organotin

1mL Ethyl Acetate

0.5mL Ethanol

1mL Ethyl Acetate 1mL DMF

12g Distilled Water

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6. Results

6.1 Degradation Analysis

The organotin displayed different behaviors during degradation depending upon

the temperature being applied. At the lower temperatures (175 C and 200 C) the

organometallic powder melted to form a clear/white liquid with many air bubbles of both

large and small sizes. As time went on and the heating continued, the liquid changed to a

brownish, gold color, a change most likely caused by oxidation, and the air bubbles

remained. During cooling, these liquids solidified into very brittle, glassy surfaces in 10

to 30 seconds. This liquid to solid behavior continued until the sample had sufficiently

degraded to the point such that it took the form of brittle, brown flakes. These flakes held

their structure under heating but their color changed to dark brown by the end of the test.

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Degradation at these temperatures was also very slow, taking as along as 36 hours just to

achieve ~35.5% weight loss, as seen in figure 19.

Degradation at 200 C

0

5

10

15

20

25

30

35

40

0 500 1000 1500 2000 2500

Time (min)

% W

eig

ht

Lo

ss

When samples were degraded at 300 C and above, degradation happened much

faster than at temperatures below the melting point of tin (231 C). Peak weight loss was

found to be between 41% and 48% and the time taken to reach maximum degradation

was fairly consistent among all temperatures at or above 300 C as shown in Figure 20.

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Degradation of Organotin

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35

Time (min)

% W

eig

ht

Lo

ss

200 C

300 C

400 C

500 C

600 C

Degradation at these higher temperatures was also much more violent than at the lower

temperatures. Instead of melting into a viscous liquid, the sample formed a brown, flaky

bubble-like structure in less than 5 minutes. This was probably due to the speed of the

degradation causing the air bubbles to inflate the sample in its liquid state, instead of

slowly escaping over time. The sample then lost its structure and became a mix of gray

and black flakes and powder, almost resembling ash. Figure 21 summarizes the

degradation of the organometallic powder at different percent weight losses.

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The data collected and visual observations made during the degradation tests at

the lower temperatures suggest that heating the electrospun organometallic at or below

200 C would be insufficient. The degradation occurs much too slowly to be acceptable if

metallic fibers were to ever be manufactured with this method and material. The

organometallic could not reach maximum degradation even after 36 hours of heating.

The fact that the organometallic becomes liquid suggests that any fibrous structure

produced during the initial electrospinning process would lose their form under heating

and spread out across the surface of the aluminum foil collection plate.

300 C seemed to be the ideal temperature for degrading the samples because it

allowed the organometallic to reach maximum degradation within a relatively short

amount of time. Temperatures higher than 300 C also reached maximum degradation but

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the samples seemed to react much more violently, as suggested by the amount of residue

on the side of the aluminum cups. These violent reactions are also the likely cause of the

weight loss measurements being consistently larger at the higher temperatures. These

discrepancies were due to material being thrown out of the aluminum containers.

Tabulated data of all weight loss tests can be viewed in the appendix.

6.1.1 Differential Scanning Calorimeter

The DSC data in Figure 22 shows a peak at 110.73 C, which represents degradation due

to water loss.

The amount of weight loss due to water evaporating can be calculated by taking the area

of the peak and dividing by the delta H of water, 40.65 kJ/mol.

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2.86% of the total mass loss of this sample was due to the evaporation of water.

The graph also confirms that degradation of the powder occurs between 250 C and 300 C,

which corresponds to conclusions made from the previous test.

Similarly, mass loss due to the evaporation of water for the 3.3mg sample is calculated as:

2.78% of the total mass loss was caused by water, which closely matches the water loss

from the 3.1mg sample.

The graph shows agreement with both the first DSC graph and the furnace test that

degradation powder degradation begins between 250 C and 300 C.

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6.1.2 X-Ray Diffraction

X-Ray Diffraction for 300 C Degradation

0

500

1000

1500

2000

2500

3000

3500

4000

0 20 40 60 80 100 120 140 160

2-Theta

Inte

ns

ity

XRD analysis revealed only peaks for aluminum which was used to hold the degraded

sample.

Since the amounts of organotin present in all of the electrospun solutions were so small, it

was decided that EDS analysis would be best for determining the composition of the

samples before and after degradation.

6.2 Electrospinning

Before the electrospinning could take place, the various solutions had to be

prepared. Butyltin chloride dihydroxide was not soluble in water; in fact it did not even

get the powder wet. Murikami et al. [20] cited ethanol as the solvent used to dissolve

several different organotin compounds. Ethanol had the identical reaction as water to the

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organotin chosen for this experiment. Several different organic solvents were tested

including chloroform, tetrahydrofuran (THF), Dimethylformamide (DMF), and ethyl

acetate. Chloroform, THF and DMF mixtures appeared to form slurries rather than

solutions and most of the organometallic powder eventually precipitate out of the solvent

and settled at the bottom of the mixing beaker. Ethyl acetate also formed a cloudy,

slurry-like mixture but the powder did not readily precipitate out so it became the main

solvent used throughout most of the electrospinning trials.

6.2.1 Solution 1 - 10% PVA (Mw 146,000 – 186,000), 20% Surfactant, and 5% Organotin

The first solution attempted to use distilled water as the solvent by using a

surfactant (sodium dodecyl sulfate) to assist in the dissolution of the organotin. The

resulting mixture had visible powder particles and air bubbles. The results of the first

electrospinning attempt, using a 30 gauge syringe are shown in Figure 25.

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The organotin particles were too large for the needle, which resulted in clogging and very

little polymer getting through. The large particles also sprayed across the surface of the

collection plate instead of being contained within the polymer fibers. To help facilitate

the electrospinning process, the solution was switched into a syringe with an 18 gauge

needle.

This adjustment improved the electrospinnability of this solution, as seen in Figure 26 by

the significant increase in fiber density. However, the organotin can clearly be seen

laying in large chunks on top of the polymer fibers, which was not the desired result and

made the formation of metal or metal-oxide fibers unlikely.

6.2.2 Solution 2 - 8% PS (Mw 400,000), 2% Organotin in 1mL Ethyl Acetate

The second solution attempted to utilize the best performing solvent, ethyl acetate,

in conjunction with a low concentration of organotin in hopes of making a more

uniformly distributed solution. Polystyrene was chosen because it is also soluble in ethyl

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acetate. SEM photographs of the electrospun structure for this solution are shown in

Figure 27.

These structures, resembling beads connected by a string, seemed to show a potentially

successful trial but upon degradation at 300 C for 15 minutes, the SEM showed the

following:

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The pictures do not clearly show the formation of any new structures, metallic or

otherwise. Figures 29 and 30 show EDS data of this solution before and after

degradation.

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Before degradation, the scan primarily detects the aluminum background and the carbon

in the polymer and the organometallic along with trace amounts of tin. After degradation,

the scan detects a large amount of carbon residue covering the surface of the sample. The

peaks corresponding to tin are more pronounced and there is an oxygen peak, suggesting

the formation of an oxide, most likely tin oxide. The carbon residue makes detecting any

tin structures on the SEM photographs impossible but the EDS does confirm that tin is

present.

6.2.3 Solution 3 - 0.5% Organotin in 1mL Ethyl Acetate

This solution attempted to reduce the amount of undissolved particles in the slurry

by reducing the amount of organotin and using the best solvent, ethyl acetate.

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The mixture lacked the appropriate viscosity for electrospinning, resulting in the

formation of structures resembling water droplets. While some of these droplets contain

the organotin, the 100x photo clearly shows large, undissolved particles laying on the

surface of the aluminum.

After the sample was degraded at 300 C for 15 minutes, the vast majority of the

aluminum background was completely bare. However, on one sample, shown in Figure

32, a single structure remained.

35

The structure shown was likely the result of a large droplet or undissolved powder

particle exploding during heating and forming this crystallized residue. It appears to be a

unique case as similar behavior was not seen on other parts of this sample nor was a

structure like this seen on any of the other electrospun solutions.

6.2.4 Solution 4 – 2% Organotin in 0.4 HCl and 0.5 Ethanol

This mixture attempted to use hydrochloric acid to break down the organometallic

compound and assist in dissolution. Ethanol was added to the organotin with no effect.

The introduction of the HCl to the mixture caused the powder to completely dissolve

after approximately 10 minutes of stirring. Upon electrospinning, no sample was

collected on the aluminum plate. The solution may have completely evaporated when

traveling between the needle and the collection plate, but the definite cause for the failure

of this trial is unknown. SEM analysis showed a completely bare aluminum plate.

6.2.5 Solution 5 - 12% PS (Mw 400,000), 2% Organotin, 1mL Ethyl Acetate

According to one study, increasing the concentration of polystyrene in solution

can cause the electrospun structure to transition from beads, to beads-on-a-string, and

finally bead-free fibers [4]. This mixture maintained the same concentrations of

organotin and ethyl acetate as in solution 2 but increased the concentration of PS by 4%.

The resulting electrospun structures are show in Figure 33.

36

The SEM pictures show similar structures as those formed by solution 2. The beads look

more elongated than those in solution 2 suggesting the transition to bead-free fibers.

Degradation of this sample at 300 C for 15 minutes resulted in no observable metal or

metal-oxide structures being formed.

37

6.2.6 Solution 6 - 5% Organotin in 1mL Ethyl Acetate

This mixture is a modification of solution 3. The concentration of organotin was

increased from 0.5% to 5% in order to investigate its effect on the electrospun structure.

Figures 34a and 34b show that the concentration of the droplet structures increased

significantly. The droplets also appear more “solid” than in solution 3, suggesting the

presence of more organotin. Figures 34b and 34c also show that many of the droplets

have long tails, which could mean that a transition to “beads-on-a-string” began to occur.

38

Degradation of this sample at 300 C for 15 minutes produced a bare aluminum

surface.

6.2.7 Solution 7 - 2% Organotin in 0.2mL HCl and 1mL Dimethylformamide

This solution was another attempt at breaking down the organotin with acid and

dissolving it in one of the less effective organic solvents. Upon electrospinning, this

solution did not stick to the collection plate. Liquid collected and slid down the face of

the aluminum. This was likely caused by the solvent not evaporating while in transit

between the syringe and collection plate. Nonetheless, viable samples were still obtained

from the area around where the solvent dripped.

Even before SEM analysis, small white particles of the powder were visible on

the collection plate. However, they appeared much smaller than the particles seen before

the solution was mixed proving the acid had effectively broken down the organotin.

39

The SEM shows a series of particles with complex structures sprayed across the surface

of the aluminum. These are simply small particles of the organotin powder. While this

mixture was not very electrospinnable, it did show that the organometallic could be

broken down into smaller particles, information that could prove useful in later studies.

If these smaller particles could be combined with a polymer, a more viable mixture could

result as these particles can more easily fit inside of the polymer fibers. A sufficient

quantity of these organotin particles inside the polymer fiber could result in the formation

of a chain of metal or metal-oxide upon degradation.

40

Figure 36 shows SEM photographs of solution 7 after degradation at 300 C for 15

minutes.

The particles appear to have more uniform structuring and are smaller than the particles

seen before degradation took place. This confirms that the organotin lost mass as

intended but because the solution sprayed out of the needle instead of being extruded as a

fiber, there was no opportunity for more complex structures to form.

8. Conclusion and Future Work

An organometallic that met the selection criteria was successfully chosen and

analyzed. The degradation analysis showed that the peak weight loss of butyltin chloride

dihydroxide was ~43% and the ideal degradation temperature was approximately 300 C.

This result was confirmed by data from the differential scanning calorimeter, which also

revealed that ~2.8% of total weight loss was due to the evaporation of water. Unique

microstructures were produced by electrospinning different types of solutions. Polymer-

based solutions showed a much higher degree of electrospinnability but left significant

41

carbon residue upon degradation. The solvent-based solutions showed the formation of

droplet structures, which could be useful as a vehicle for applying organometallic

coatings on a material. The use of acid to break down the organometallic shows promise

but more trials need to be done to fully explore this option.

EDS analysis confirmed the presence of tin and tin oxide particles after thermal

degradation of electrospun structures. Additives may be necessary to bind the

organometallic particles together to facilitate the formation of continuous or

discontinuous fibers. If an effective solvent could be found that would increase the wt%

of organotin in solution to 15-20%, instead of 0.5-5, particle interaction would

significantly increase, which would promote the formation of tin nanostructures.

Future research for this project should focus on solvent interactions with the

organometallic rather than the degradation behavior. The formation of homogeneous

solutions is vital to the electrospinning process, as seen by past successes. The possibility

of alloying two or more metals by means of electrospinning organometallics with

different base metals should also be examined.

42

References

1. Cao, Guozhong Nanostructures and Nanomaterials - Synthesis, Properties and

Applications. null.

2. T. J. Sill, H. A. von Recum, Biomaterials 29 (2008) 1989-2006

3. T. Jarusuwannapoom, W. Hongrojjanawiwat, S. Jitjaicham, L. Wannatong, M.

Nithitanakul, C. Pattamaprom, P. Koombhongse, R. Rangkupan, P. Supaphol,

European Polymer Journal 41 (2005) 409-421

4. G. Eda, Effects of Solution Rheology on Electrospinning of Polystyrene, April

2006

5. Lee, Stuart M. Handbook of Composite Reinforcements (pp 364, 405-417). John

Wiley & Sons.

6. M. J. Koczak, S. C. Khatri, J. E. Allison, M. G. Bader, Metal-Matrix Composites

for Ground Vehicle, Aerospace and Industrial Applications

7. H. Jang, K. Ko, S.J. Kim, R.H. Basch, J.W. Fash, Wear 256 (2004) 406-414

8. L. Tadrist, M. Miscevic, O. Rahli, F. Topin, Experimental Thermal and Fluid

Science 28 (2004) 193–199

9. K. M. Lee, Y. S. Lee, Y. M. Jo, J. Air & Waste Manage. Assoc. 56:1139-1145

10. Kalpakjian, Serope, Manufacturing Engineering and Technology – 4th

Edition.

2001, Prentice-Hall Inc, New Jersey

11. Lewis, Richard J., Sr. (2002). Hawley's Condensed Chemical Dictionary (14th

Edition). John Wiley & Sons.

12 Notargiacomo, E. Giovine, F. Evangelisti, V. Foglietti, R. Leoni, Mat. Sci. and

Eng. C 19 (2002) 185-188

13 L Bernard, M Calame, S J van der Molen, J Liao, C Schonenberger,

Nanotechnology 18 (2007) 235202 (6pp)

14 H. Xu, D. Qin, Z. Yang, H. Li, Materials Chemistry and Physics 80 (2003) 524-

528

15 H. Y. Dang, J. Wang, S. S. Fan, Nanotechnology 14 (2003) 738-741

16 M. S. Silberberg, Chemistry – The Molecular Nature of Matter and Change, 4th

Edition. 1945 – McGraw Hill publishing

43

17 G. E. Coates, M. L. H. Green, P. Powel, K. Wade, Principles of Organometallic

Chemistry. 1968 Methuen & Co. Ltd.

18 J. S. Thayer, Organometallic Chemistry, an overview. 1988 VCH Publishers, Inc.

New York, NY

19 Y. Wang, M. Aponte, N. Leon, I. Ramos, R. Furlan, N. Pinto, J. Am. Ceram. Soc.

88 (8) 2056-2063 (2005)

20 K. Murakami, I. Yagi, S. Kaneko, J. Am. Ceram. Soc. 79 [10] 2557-62 (1996)

44

Appendix A Data from degradation analysis


T = 175C Container Wt Total Initial Wt. Initial Sample Wt

2.5707 6.652 4.0813

Time Total Weight Sample Weight % Wt. Loss

0 6.652 4.0813 0

60 6.2485 3.6778 9.886555754

90 6.206 3.6353 10.92789062

120 6.1651 3.5944 11.9300223

150 6.128 3.5573 12.83904638



3.1934 7.619 4.4256


0 7.619 4.4256 0

10 7.3299 4.1365 6.532447578

20 7.2476 4.0542 8.39208243

30 7.2099 4.0165 9.243944324

40 7.1802 3.9868 9.915039769

50 7.149 3.9556 10.62002892

60 7.1157 3.9223 11.37246927

90 7.0543 3.8609 12.75985177



2.71 6.8666 4.1566


0 6.8666 4.1566 0

5 6.6191 3.9091 5.954385796

10 6.527 3.817 8.170139056

15 6.4791 3.7691 9.322523216

20 6.448 3.738 10.07073089

25 6.4103 3.7003 10.97772218

30 6.3805 3.6705 11.69465428

35 6.3681 3.6581 11.99297503

40 6.3402 3.6302 12.6641967

50 6.2937 3.5837 13.78289949

60 6.2551 3.5451 14.71154309

70 6.2196 3.5096 15.56560651

45



1.0453 1.2116 0.1663


0 1.2116 0.1663 0

5 1.1928 0.1475 11.30487072

10 1.187 0.1417 14.7925436

15 1.1812 0.1359 18.28021648

20 1.1758 0.1305 21.52736019

25 1.169 0.1237 25.61635598

30 1.1643 0.119 28.44257366

35 1.1608 0.1155 30.54720385

45 1.1584 0.1131 31.99037883

50 1.1575 0.1122 32.53156945

60 1.1555 0.1102 33.73421527

75 1.1535 0.1082 34.93686109

90 1.1522 0.1069 35.71858088

105 1.151 0.1057 36.44016837

120 1.1493 0.104 37.46241732

150 1.1478 0.1025 38.36440168

167 1.1477 0.1024 38.42453397

182 1.1473 0.102 38.66506314

192 1.1472 0.1019 38.72519543



1.1492 1.2905 0.1413


0 1.2905 0.1413 0

5 1.234 0.0848 39.98584572

10 1.2301 0.0809 42.74593064

15 1.2301 0.0809 42.74593064

20 1.2305 0.0813 42.46284501

25 1.2305 0.0813 42.46284501

30 1.2303 0.0811 42.60438783

46



3.153 7.3225 4.1695


0 7.3225 4.1695 0

10 5.7525 2.5995 37.65439501

15 5.421 2.268 45.60498861

20 5.4343 2.2813 45.28600552

25 5.434 2.281 45.29320062

30 5.435 2.282 45.26921693


T = 300C Container Wt. Total Initial Wt. Initial Sample

1.8819 5.594 3.7121

Time Total Weight Sample Weight % Wt Loss

0 5.594 3.7121 0

10 4.418 2.5361 31.68018103

20 3.9944 2.1125 43.09151154

30 3.9987 2.1168 42.97567415

Degradation at 300 C T =

300C Container

Wt. Total Wt. Time Sample Wt.

% Wt. Loss

2.6364 3.4107 0 0.7743 0

3.2264 5 0.59 23.80

3.1545 10 0.5181 33.09


350C Container


% Wt. Loss

2.2401 2.8747 0 0.6346 0

2.5868 5 0.3467 45.37

2.5842 10 0.3441 45.78



0.8897 1.0099 0.1413


0 1.0099 0.1413 0

5 0.9537 0.0848 39.98584572

10 0.9532 0.0809 42.74593064

15 0.9532 0.0809 42.74593064

20 0.9528 0.0813 42.46284501

25 0.9528 0.0813 42.46284501

47


400C Container


% Wt. Loss

2.1028 2.896 0 0.7932

2.5143 5 0.4115 48.12

2.513 10 0.4102 48.29


400C Container


% Wt. Loss

1.8646 2.5014 0 0.6368

2.2053 5 0.3407 46.50

2.2029 10 0.3383 46.88



1.0999 1.191 0.0911


0 1.191 0.0911 0

5 1.1484 0.0485 46.76180022

10 1.1484 0.0485 46.76180022

15 1.1485 0.0486 46.65203074

25 1.1487 0.0488 46.43249177



1.0227 1.1555 0.1328


0 1.1555 0.1328 0

5 1.0912 0.0685 48.4186747

10 1.091 0.0683 48.56927711

15 1.0909 0.0682 48.64457831

20 1.091 0.0683 48.56927711



0.9828 1.06 0.0772


0 1.06 0.0772 0

5 1.0235 0.0407 47.27979275

10 1.0232 0.0404 47.66839378

15 1.0231 0.0403 47.79792746

20 1.0232 0.0404 47.66839378

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